I have a 1966 Buick Skylark (non-GS) and ordered this diagram as what was in my reproduced shop manual was grainy and b&W. Also, the best I could find online was in color but wouldn't print large enough to be really legible.
I ordered this diagram out of blind hope that it would be the answer to my needs- and it has been :) You can tell that they redrew it, but I can't find where it misses the original at all.
I got the big version and it goes great on the windshield while doing re-wiring with the hood off. It is big enough and clear enough that I can lean in a bit from either fender and make out what goes where. I would definitely buy again.